1. Field of the Invention
The present invention relates to a substrate processing method of processing a substrate with a low surface tension liquid. Examples of the substrate to be processed include substrates such as semiconductor wafers, glass substrates for liquid crystal display devices, substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates and substrates for solar cell.
2. Description of Related Art
In the manufacturing processes of semiconductor devices, processing using a processing liquid is performed on a front surface of substrates such as semiconductor wafer. A single substrate processing type substrate processing apparatus that processes a single at a time substrate includes a spin chuck that rotates the substrate while holding the substrate substantially horizontally and a nozzle that supplies the processing liquid to the front surface of the substrate rotated by the spin chuck.
In a typical substrate processing step, a chemical liquid is supplied to the substrate held by the spin chuck. Thereafter, a rinse liquid is supplied to the substrate, and thus the chemical liquid on the substrate is replaced with the rinse liquid. Then, a spin dry step that removes the rinse liquid on the substrate is performed. In the spin dry step, the substrate is rotated at a high speed, and thus the rinse liquid adhered to the substrate is removed (dried) by being spun off. In general, the rinse liquid is deionized water.
When a fine pattern is formed on the front surface of the substrate, in the spin dry step, the rinse liquid entering the pattern may not be removed, and thus a drying failure may occur. Hence, a method is proposed in which an organic solvent such as isopropyl alcohol (IPA) is supplied to the front surface of the substrate after being processed with the rinse liquid, in which the rinse liquid entering the gap of the pattern on the front surface of the substrate is replaced with the organic solvent and in which the front surface of the substrate is dried.
As shown in FIG. 17, in the spin dry step in which the substrate is dried by rotating the substrate at a high speed, a liquid surface (interface between air and the liquid) is formed within the pattern. In this case, the surface tension of the liquid is exerted on the contact position of the liquid surface and the pattern. The surface tension is one of the causes that collapse the pattern.
As disclosed in Japanese Patent Application Publication No. 2009-212301, when after rinse processing, the liquid of an organic solvent is supplied to the front surface of the substrate before a spin dry step, the liquid of the organic solvent enters a pattern. The surface tension of the organic solvent is lower than that of water such as a typical rinse liquid. Hence, the problem in which the pattern is collapsed by the surface tension is alleviated.
In the method disclosed in Japanese Patent Application Publication No. 2009-212301, in order to enhance the replaceability of the rinse liquid with the organic solvent, not only is the organic solvent supplied to the front surface of the substrate but also a heating liquid is supplied to the rear surface on the Side opposite to the front surface of the substrate.
In the method disclosed in Japanese Patent Application Publication No. 2009-212301, in a state in which the supply of the heating liquid to the rear surface of the substrate is stopped, the supply of the organic solvent to the front surface of the substrate is continued for a predetermined period of time. During the period of time, the supply of the organic solvent to the substrate is continued, and the heat of the substrate is removed by the organic solvent which is additionally supplied. Hence, a significant heat loss occurs in the substrate. Furthermore, the heating of the substrate by the heating liquid is stopped. Thus, the temperature of the substrate is gradually lowered. Thereafter, the spin dry step is started. Hence, in the present method, the spin dry step is started on the substrate whose temperature is lowered. Although in the spin dry step, a low surface tension liquid entering the pattern on the front surface of the substrate needs to be spun off by centrifugal force resulting from the rotation of the substrate, when the spin dry step is started in a state in which the substrate has a low temperature, it takes a long period of time to perform the spin dry step. When it takes a long period of time to perform the spin dry step, the impulse of the surface tension of the low surface tension liquid acting on the pattern is increased, with the result that this contributes to the collapse of the pattern.
Hence, an object of the present invention is to provide a substrate processing method that can effectively reduce the collapse of a pattern.
According to the invention, there is provided a substrate processing apparatus including a replacement step of replacing a rinse liquid adhered to a front surface of a substrate with a low surface tension liquid whose surface tension is lower than a surface tension of the rinse liquid and a spin dry step of rotating, after completion of the replacement step, the substrate about a predetermined rotation axis to spin off the low surface tension liquid so as to dry the front surface, where the replacement step includes a low surface tension liquid supply step of supplying the low surface tension liquid to the front surface while supplying a heating fluid to a rear surface on a side opposite to the front surface and a post-heating step of supplying the heating fluid to the rear surface on the side opposite to the front surface of the substrate, in a state in which the supply of the low surface tension liquid to the front surface is stopped, before start of the spin dry step after completion of the low surface tension liquid supply step.
According to the method, in the post-heating step after the low surface tension liquid supply step, the supply of the low surface tension liquid to the front surface of the substrate is stopped, and thus the heat of the substrate is prevented from being removed by the low surface tension liquid supplied additionally. In this state, the heating liquid is supplied to the lower surface of the substrate to heat the substrate. In this way, it is possible to start the spin dry step on the substrate at a high temperature. Hence, the spin dry step can be completed in a short period of time. If the spin dry step can be completed in a short period of time, it is possible to restrict the impulse of the surface tension acting on the pattern at a small level. In this way, it is possible to more effectively reduce the collapse of the pattern at the time of the spin dry step.
The heating fluid may be a liquid (heating liquid) or a gas (heating gas). An example of the heating liquid is water. An example of the heating gas is an inert gas and water vapor. The heating fluid may be supplied to the entire rear surface or may be supplied to part of the rear surface.
In a preferred embodiment of the invention, the post-heating step and the spin dry step are continuously performed.
According to the method, the temperature of the substrate at the start of the spin dry step can be further increased. Hence, it is possible to complete the spin dry step in a shorter period of time.
In the spin dry step, the heating fluid may be supplied to the rear surface of the substrate.
According to the method, the temperature of the substrate when performing the spin dry step can be further increased. Hence, it is possible to complete the spin dry step in a shorter period of time.
The substrate processing method may further include a paddle step of bringing the substrate into a stationary state or rotating the substrate about the rotation axis at a paddle speed in parallel with the post-heating step.
According to the method, in the paddle step, on the upper surface of the substrate, the liquid film of the low surface tension liquid covering the upper surface is supported so as to be formed in the shape of a paddle. Hence, before the start of the spin dry step, the front surface of the substrate can be prevented from being exposed from the liquid film. When the front surface of the substrate is partially exposed, the cleanliness of the substrate may be lowered by particle generation, and the uniformity of the processing may be lowered. However, the front surface of the substrate can be prevented from being exposed from the liquid film, and thus it is possible to prevent the lowering of the cleanliness of the substrate and the lowering of the uniformity of the processing.
The post-heating step may include a step of discharging the heating fluid simultaneously to the rear surface from a plurality of heating fluid discharge ports aligned along a radial direction of the rotation of the substrate.
According to the method, the heating fluid is discharged to the rear surface of the substrate from a plurality of heating fluid discharge ports aligned along the radial direction of the rotation of the substrate. In parallel with discharging the heating fluid from the heating fluid discharge ports, the substrate is rotated, and thus it is possible to supply the heating fluid to the entire rear surface of the substrate. Hence, in the post-heating step, the liquid film of the low surface tension liquid can be heated in the entire front surface of the substrate. In this way, it is possible to effectively reduce the collapse of the pattern in the entire front surface of the substrate.
The post-heating step may include a step of discharging the heating fluid to the rear surface in a direction intersecting the radial direction of the rotation of the substrate when seen in a direction perpendicularly intersecting the rotation axis.
According to the method, the heating fluid discharged to the lower surface of the substrate is unlikely to flow around onto the upper surface of the substrate.
The heating fluid may include a heating liquid, and the flow rate of the heating liquid in the post-heating step may be set such that the heating fluid supplied to the rear surface of the substrate is prevented from flowing around onto the front surface.
According to the method, the flow rate of the heating liquid supplied to the rear surface of the substrate is set such that the heating fluid is prevented from flowing around onto the front surface of the substrate. Hence, even when in the post-heating step, the supply of the low surface tension liquid to the front surface of the substrate is stopped, it is possible to heat the liquid film of the low surface tension liquid while reliably preventing the low surface tension liquid from flowing around onto the front surface of the substrate at a high temperature.
The low surface tension liquid supply step may include a step of discharging the low surface tension liquid from a low surface tension liquid nozzle which is located above the front surface of the substrate, the spin dry step may be performed in a state in which an opposite member is opposite above the front surface of the substrate and in parallel with the post-heating step, the low surface tension liquid nozzle may be retracted from above the substrate, and the opposite member may be located above the substrate.
According to the method, in parallel with the post-heating step, the low surface tension liquid nozzle is retracted from above the substrate, and the opposite member is located above the substrate. Since even in the period of the retraction and the arrangement, the supply of the heating fluid to the rear surface of the substrate is continued, it is possible to heat the liquid film of the low surface tension liquid until immediately before the start of the spin dry step.
The low surface tension liquid supply step may include a droplet supply step of supplying a droplet of an organic solvent produced by mixing the organic solvent with a gas to at least an outer circumferential portion of the front surface.
According to the method, the droplet of the low surface tension liquid is supplied to at least the outer circumferential portion of the front surface of the substrate. A physical force is applied by the collision of the droplets of the organic solvent to the supply region of the droplets of the organic solvent on the front surface of the substrate. Thus, it is possible to further enhance the performance of the replacement with the low surface tension liquid.
In general, the performance of the replacement with the organic solvent in the outer circumferential portion of the front surface of the substrate is considered to be low. However, the droplets of the low surface tension liquid are supplied to at least the outer circumferential portion of the front surface, and thus it is possible to improve the performance of the replacement with the organic solvent in the outer circumferential portion of the front surface of the substrate.
The droplet supply step may include a droplet discharge step of discharging the droplet of the organic solvent from a two-fluid nozzle to a discharge region within the front surface and a discharge region movement step of moving the discharge region between a center portion of the front surface and a circumferential edge portion of the front surface in parallel with the droplet discharge step.
According to the method, it is possible to enhance the performance of the replacement with the low surface tension liquid in the entire front surface of the substrate.
The low surface tension liquid supply step may include a first liquid film formation step which is performed before the droplet discharge step and which supplies the organic solvent to the front surface so as to form a liquid film of the organic solvent covering the entire front surface.
According to the method, before the supply of the droplets to the front surface of the substrate from the two-fluid nozzle, the liquid film of the low surface tension liquid covering the entire front surface of the substrate is formed. Hence, the droplets of the low surface tension liquid discharged from the two-fluid nozzle collide with the liquid film of the organic solvent. Thus, it is possible to prevent the droplets of the low surface tension liquid from directly colliding with the front surface of the substrate in a dry state, with the result that it is possible to reduce particle generation.
The low surface tension liquid supply step may include a second liquid film formation step which is performed after the droplet discharge step and which supplies the organic solvent to the front surface so as to form a liquid film of the organic solvent covering the entire front surface.
According to the method, after the droplet discharge step, the liquid film of the low surface tension liquid covering the front surface is held on the front surface of the substrate. Hence, before the start of the spin dry step, the front surface of the substrate can be prevented from being exposed from the liquid film. When the front surface of the substrate is partially exposed, the cleanliness of the substrate may be lowered by particle generation, and the uniformity of the processing may be lowered. However, the front surface of the substrate can be prevented from being exposed from the liquid film, and thus it is possible to prevent the lowering of the cleanliness of the substrate and the lowering of the uniformity of the processing.
The spin dry step may be performed while an atmosphere around the front surface is maintained to be an atmosphere of nitrogen.
According to the method, since the front surface can be dried while the atmosphere around the front surface of the substrate is maintained to be the atmosphere of nitrogen, it is possible to reduce or prevent watermark generation after the drying.
The objects, the features and the effects in the present invention described above or still other objects, features and effects will be more apparent from the following description of preferred embodiments with reference to the accompanying drawings.